Commercial airlines perform tens of millions of takeoffs annually. Only a very small percentage of attempted takeoffs result in rejected takeoffs (RTO's). Pilots decide to execute RTO's due to a variety of factors including engine failure, wheel/tire failure, incorrect pre-flight configuration, indicator/warning lights, lack of crew coordination, and bird strikes. An RTO at a low speed rarely results in any adverse consequences. High-speed RTO's, on the other hand, can potentially cause the airplane to overrun the end of the runway, with catastrophic consequences. See Federal Aviation Administration, “Pilot Guide to Takeoff Safety”, retrieved from https://www.faa.gov/other_visit/aviation_industry/airline_operators/training/media/takeoff_safety.pdf
A recurring issue in aviation is errors in aircraft dispatch and/or the incorrect pilot inputs of takeoff parameters. Before takeoff, the flight control computer is typically initialized with certain parameters pertinent to the takeoff. These inputs include weight, configuration (flap position), thrust and takeoff speeds (V1, VR and V2). Since thrust and V speeds are critical to proper takeoff, errors in inputting these parameters can lead to serious aircraft accidents. The table below presented some accidents related to wrong takeoff data:
Fatal-Registra-itiesDateTypetionOperatorLocation27125-May-1979DC-10-10N110AAA AirlinesUSA24827-Mar-1977Boeing 747PH-BUFKLMSpain15416-Aug-1987DC-9-82N312RCNorthwest USAAirlines15420-Aug-2008DC-9-82EC-HFPSpanairSpain14125-Dec-2003Boeing 7273X-GDOUTABenin1303-Jun-1962Boeing 707F-BHSMAir FranceFrance1108-Oct-2001DC-9-87SE-DMASASItaly 8331-Oct-2000Boeing 7479V-SPKSingapore TaiwanAirlines 8228-Aug-1993Yakov 4087995Tajikistan TajikistanAirlines
Such types of accidents are often consequences of a lower aircraft capability to accelerate and/or climb. A particularly terrible example where an accident was related to wrong takeoff configuration (and overweight) is the case of Union des Transports Africains de Guinée (UTA) Flight 141 which departed Conakry, Guinea for a scheduled flight to Beirut, Lebanon on Christmas Day, Dec. 25, 2003. The Boeing 727 departed at 10:07 carrying 86 passengers and a crew of 10. It arrived at Cotonou at 12:25 where nine passengers disembarked. A total of 63 people had checked in at the Cotonou airport check-in-desk. Ten others boarded from a flight that had arrived from another airport. Passenger boarding and baggage loading took place in a climate of great confusion. The plane was full and it is thought that there were more passengers aboard the plane than had officially checked in.
The flight crew began pre-flight checklist at 13:47 and were cleared to roll at 13:52. Passengers were still standing in the aisles at that time. At 13:58:01, the thrust lever was advanced, 14 seconds later the brakes were released and the Boeing 727 began accelerating down the runway. 46 seconds after the brakes were released, the captained announced V1 and VR speeds. At that moment the aircraft was 1620 meters down the runway at a speed of 137 knots.
The co-pilot pulled back on the control column to rotate the plane at VR. This action initially had no effect on the airplane's angle of attack. The Captain called “Rotate, rotate”, and the co-pilot pulled back harder. The angle of attack only increased slowly. The pilot did not command an RTO. Seven seconds later, at a speed of 148 knots and 2100 meters down the runway, the nose just slowly rose. The 727 barely climbed away from the ground, causing its main undercarriage to strike localizer antennas at the end of the runway and strike a 3-meter-high small building housing radio equipment. The plane continued beyond the end of the runway, smashing through a concrete airport boundary fence and slamming into the beach. The fuselage broke into several pieces. At least 144 people died in the crash.
The official explanation of the crash was that the aircraft's weight exceeded its maximum weight capacity. The accident resulted from difficulty that the flight crew encountered in performing rotation with an overloaded airplane whose forward center of gravity was unknown to them.
To avoid such disasters, the preflight operational engineer typically carefully calculates the takeoff weight (TOW) of the aircraft based on a weight & balance spreadsheet. The spreadsheet and/or calculation presents some statistical simplifications which decrease the level of accuracy. An example is the passenger estimated weight that can significantly differ from the real one. The same can be related to the baggage and other cargo.
The takeoff “Vspeeds” (V1, VR, V2) evaluation is based on the takeoff weight. Therefore, if the weight is wrong, so are the takeoff speeds. It is also possible to incorrectly calculate the V-speeds even if the weight determination is right. Even if the operational engineer's calculations are all correct, the pilot and/or dispatch inputs into the flight computer can be wrong.
Today, the only way to confirm if the data is right is to recalculate and/or re-check the input data. This is of course not a failure-proof processes.
Some in the past have proposed ways to monitor if the data are correct and, in case of a detected error, alert the pilot to make some action. But since the pilot workload is higher at takeoff, such proposals must somehow assure that there is enough runway remaining to stop the aircraft without a runway excursion (overrun) in case the pilot decides to abort the takeoff.
Although such prior techniques propose a way to check if there are some errors on dispatch, they all introduce a higher pilot workload, since the pilot must understand the situation and must decide to make the first action to abort the takeoff.